Multi-disc brake actuator for vibration damping

ABSTRACT

A multi-disc brake (80) includes a piston housing (102) and attached torque tube (94) located about an axle (87). Integrated within the piston housing (102) is a brake actuator (90). The piston housing (102) is located axially between an actuator member (98) of the brake actuator (90) and an axle sleeve (109) and radial portion 87a of the axle (87). Hydraulic actuation of the brake actuator (90) displaces axially the actuator member (98) against a stationary thrust sleeve (99) such that the piston housing (102) is compressed between the actuator member (98) and axle sleeve (109), thereby reducing torsional vibrational movement of the piston housing (102) and torque tube (94) about the axle (87).

This is a continuation-in-part of patent application Ser. No. 08/626,660filed Mar. 22, 1996.

The present invention relates generally to a multi-disc brake, and inparticular to a brake actuator which reduces torsional vibrations of themulti-disc brake.

Multi-disc brakes have been used on aircraft for many years. Typically,such multi-disc brakes include a piston housing attached to a torquetube, each disposed about an axle of the aircraft, with a plurality ofstator discs engaging the torque tube and an interleaved plurality ofrotor discs attached to the surrounding wheel which is mountedrotatability upon the axle. Many multi-disc aircraft brakes are designedto rotate slightly about an axle when the landing gear of the aircraftis being retracted or extended. Such brakes usually have braking torquetake-out via a brake arm or other such attachment to the landing gear ofthe aircraft. During braking, it is possible for the braking torquetransmitted through the brake structure to the torque take-out mechanismto cause torsional vibration, what is known as "squeal" vibration, ofthe brake which may be described simply as rotational oscillation of thebrake relative to the axle. Such squeal vibration can occur typically atdifferent frequencies, and result in higher than normal loads beingexerted upon the braking torque take-out mechanism which typicallyinclude brake rods. The higher brake rod loads can be as many as fivetimes higher than normally experienced, and can result in the pistonhousing being detached from the brake rod of the torque take-outmechanism. Such problems can result in unscheduled removals of thebrake, an "airplane-on-the-ground" status whereby the aircraft cannotfly, and even an air worthiness directive concerning maintenance andinspection of the aircraft.

Investigation of squeal vibration modes indicates that one solution tothe problem is to increase coulomb damping, that is, rubbing or slidingfriction between two surfaces in order to provide damping in the brake.Brake vibration problems can be improved by reducing the tolerancesbetween adjacent parts of the brake assembly, but this may be dependentupon the structure of the particular brake assembly and can be subjectto the wear of the adjacent parts. In many cases, a tight controlclearance simply shifts the vibration frequency to a different level andyields unacceptable results. However, if coulomb damping could beprovided for the piston housing and attached torque tube, an achievablesolution to the squeal vibration problem can be accomplished. Oneobjective of the present invention is to reduce and/or eliminate squealvibration modes from multi-disc aircraft brakes, by providing coulombdamping during brake actuation. Another objective is to provide coulombdamping of the piston housing during brake actuation in order toincrease torque damping and to dissipate more energy or braking torqueduring brake operation. Another objective of the present invention is toprovide the coulomb damping by means of an axial clamping force whichclamps the piston housing in place relative to the axle and therebyincrease the amount of torque damping effected by the brake and thetorque take-out mechanism.

The present invention can accomplish solutions to the above problems byproviding a multi-disc brake and actuator for vibration damping,comprising a multi-disc brake disposed about axle means and including apiston housing engaging a torque tube, a first plurality of discsengaging the torque tube, a second plurality of discs for engagementwith a wheel, the piston housing being located axially between anactuator and a first axially stationary member at the axle means, and athrust sleeve engaging a second axially stationary member at the axlemeans, operation of the actuator causing an actuator member to extendaxially and compress the piston housing between the actuator member andfirst axially stationary member in order to reduce vibrational movementof the piston housing and torque tube relative to the axle means.

One way of carrying out the invention is described in detail below withreference to the drawings which illustrate embodiments in which:

FIG. 1 is a section view of a multi-disc aircraft brake which includesthe brake actuator of the present invention;

FIG. 2 is an enlarged cross-sectional view of the brake actuator of thepresent invention;

FIG. 3 is a section view of a multi-disc aircraft brake which includes asecond embodiment of the brake actuator of the present invention; and

FIG. 4 is a section view of a multi-disc aircraft brake which includes athird embodiment of the brake actuator of the present invention.

A multi-disc brake with a brake actuator of the present invention isillustrated FIG. 1. Axle means 67 has disposed there about an axiallyinner wheel bearing assembly 12 upon which is mounted a portion of theaircraft wheel 14. Also located about axle means 67 is a typical wheelsleeve 16 which is an axially stationary member having one axial end 17abutting the inner wheel bearing assembly 12 and the other axial end 18abutting a thrust sleeve 20 and axle sleeve 19. Because the thrustsleeve 20 abuts axially the wheel sleeve 16 that abuts the stationarybearing assembly 12, the thrust sleeve 20 comprises a part of theaxially stationary member. The axle sleeve 19 and thrust sleeve 20 areboth located about axle means 67, with the axle sleeve extending axiallybeyond a piston housing of a brake assembly designated generally byreference numeral 30. It should be clearly understood that brakeassembly 30 may comprise any steel or carbon aircraft brake assembly.Such assemblies typically include a piston housing 32 attached to atorque tube 34, a plurality of stator discs 36 keyed to splines 33 oftorque tube 34, and a plurality of rotor discs 38 keyed to a not shownportion of the aircraft wheel 14. As is well known in the art, thepiston housing includes a plurality of pistons 32a which are actuatedhydraulically and extend to compress the stator discs and rotor discsbetween the pistons and backing plate 39. Piston housing 32 includes aspart or portions thereof piston housing bushings 35 and 37.

Located axially adjacent the piston housing 32 is a brake actuator 40 ofthe present invention. As shown in greater detail in FIG. 2, theactuator 40 comprises a two part actuator housing 42, 43 having thereina hydraulic brake fluid cavity 45 receiving hydraulic brake fluidthrough port 46 and line 47. The actuator piston 48 includes a seal 49and a seal backup ring 50. Actuator piston 48 engages axially a movableactuator pad or outer capsule member 52 which, like the other pads ofthe actuator 40, is annular in shape, and is threadedly attached at aninner diameter thereof to the inner capsule member 54. The outer capsulemember 52 and inner capsule member 54 provide an interior caging for afirst or internal spring means 56 comprising a plurality of Bellevillewashers which engage a load washer 58. The inner capsule member 54 hasan inner diameter extension 59 which engages an actuator member or ram59A that provides a radial position and support for the load washer 58.Actuator member 59A is disposed a clearance distance "X" from the pistonhousing bushing 35. Ram 59A has a stepped radially outer configurationso that it also supplies radial positioning and support for a secondspring means or return spring 65 which engages at its other end an innershoulder of the actuator housing pad 43.

The axle sleeve 19 extends between an axle sleeve foot 27 and sleeve end29. Sleeve foot 27 abuts the actuator housing pad 42 and sleeve end 29abuts the wheel sleeve 16. The thrust sleeve 20 abuts at one end the end18 of wheel sleeve 16 and at the other end a piston housing bushing 37.Located about thrust sleeve 20 is a typical torque tube bushing 31 whichis located at the radial inner periphery of torque tube foot 34a.

During operation of the multi-disc aircraft brake 30, pressurizedhydraulic fluid is transmitted to the pistons 32A within the pistonhousing 32. The pressurized hydraulic fluid is also transmitted to thepod 46 of the brake actuator 40. When the aircraft 30 is not operating,the axial clearance "X" is present between the piston housing bushing 35and the actuator member 59A. As pressurized hydraulic fluid is receivedwithin cavity 45 of actuator 40, the actuator piston 48 moves axially tothe right in FIGS. 1 and 2 against the outer capsule member 52. Aclearance exists between the inner diameter extension 59 of innercapsule member 54 and the actuator member 59A to ensure that loading istransmitted to the actuator member 59A via load washer 58. Return spring65 provides a low pressure limiter or threshhold mechanism such thatuntil the spring preload has been exceeded, the actuator member 59A isnot displaced axially. When the actuator housing part 43 is screwed ontoactuator part 42, the return spring 65 is preloaded between the innerlip of part 43 and the upper pad of actuator member 59A. When thehydraulic pressure exceeds a predetermined limit, such as 300 psi, thepreload of return spring 65 is exceeded and the capsule member 52 beginsto travel axially to the right, moving load washer 58 and actuatormember 59A to close up the predetermined clearance "X". As actuatormember 59A engages the piston housing bushing 35 of piston housing 32,the piston housing 32 is compressed axially between actuator member 59Aand piston housing bushing 35 on one side and the piston housing bushing37, thrust sleeve 20, wheel sleeve 16 and inner wheel bearing assembly12 on the other side. This compression or clamping of piston housing 32results in the piston housing being held in a more rotatably restrainedposition relative to axle means 10, whereby there is increased torquedamping provided during the operation of the brake and braking of theaircraft wheel. Because the brake actuator 40 provides for an increasein the dissipation of braking energy, squeal vibration modes can bereduced or eliminated and thereby reduce the high braking torque loadsexerted upon the braking torque take-out mechanism. Thus, the torsionalvibration of the brake relative to the axle means is damped and theperformance and reliability of the brake can be significantly improved.

Internal springs 56 provide a maximum load limiting mechanism such thatwhen the preload in the springs has been exceeded, springs 56 compressto limit the loads applied to the brake. When member 52 is threaded ontomember 54, the springs 56 are preloaded. When the hydraulic pressureexceeds a predetermined level, such as 500 psi, the springs 56 begin tocompress whereby shoulder 52A of member 52 moves axially to engageshoulder 43A of housing part 43. Engagement of shoulders 52A and 43Alimits the load applied by actuator member 59A to the bushing 35.

A second embodiment of the multi-disc brake with a brake actuator of thepresent invention is illustrated in FIG. 3. Similar structure isindicated by reference numerals increased by 30. Axle means 97 hasdisposed thereabout an axially inner wheel bearing assembly 42 uponwhich is mounted a portion of the aircraft wheel 44. Also located aboutaxle means 97 is a typical wheel sleeve 46 which is an axiallystationary member having one axle end 47 abutting the inner wheelbearing assembly 42 and the other axle end 48 abutting a bushingassembly 79 and axle sleeve 99. Bushing assembly 79 is part of a portionof the torque tube foot 64A and torque tube 64. The axle sleeve 49 islocated about the axle means 97, with the axle sleeve extending axiallybeyond a piston housing 62 of a brake assembly designated generally byreference numeral 60. It should be clearly understood that brakeassembly 60 may comprise any steel or carbon aircraft brake assembly.Such assemblies typically include a piston housing 62 attached to thetorque tube 64, a plurality of stator discs 66 keyed to splines 63 oftorque tube 64, and a plurality of rotor discs 68 keyed to a not shownportion of the aircraft wheel 44. As is well known in the art, thepiston housing includes a plurality of pistons 62A which are actuatedhydraulically and extend to compress the stator discs and rotor discsbetween the pistons and a backing plate.

Located axially adjacent and integrated within piston housing 62 is abrake actuator 70 of the present invention. Actuator 70 includes anactuator member or piston 89A that can extend and engage the stationaryportion 91 of axle means 97. As described for the previous embodiment ofthe present invention, pressurized hydraulic fluid transmitted to thepistons 62A of piston housing 62 is also transmitted to the brakeactuator 70 so that the actuator member 89A extends to engage thestationary portion 91 of axle means 97. A not shown orifice or otherrestriction means within the hydraulic transmission line is utilized tolimit or delay the pressure transmitted to actuator 70 such that theactuator member 89A will effect an axial force against piston housing 62that reaches its maximum value substantially when the rotors 68 arebeing compressed between the starors 66. As the actuator member 89Aextends against stationary portion 91 to displace piston housing 62slightly axially in the direction of arrow A in FIG. 3, the torque tube64 which is firmly attached to the piston housing 62 is abutted tightlyat torque tube foot 64A (via bushing assembly 79) against the stationarymember or wheel sleeve 46 adjacent torque tube foot 64A, such that thepiston housing and torque tube are rubbing respectively against thestationary portion 91 of axial means 97 and end 48 of wheel sleeve 46,thereby damping vibration and reducing or eliminating squeal vibration.The actuator 70 includes a not shown return spring, similar to thatutilized in the previous embodiment or including any other resilientmeans that effects the same function, to return the actuator member toits unpressurized position at the termination of braking. The return ofthe piston 89a to its unpressurized position can effect a slightclearance with stationary portion 91 and will ensure that the brake 60will rotate slightly relative to axle means 97 during retraction of theaircraft landing gear.

The present invention provides a mechanism for reducing or eliminatingsqueal vibration modes of a multi-disc brake. The embodiment of FIG. 1requires parts and design changes that have little impact upon thebraking system and which are easily retrofitted on existing brakeassemblies. The embodiment of FIG. 3 can be utilized when a new brakedesign is being implemented and an integrated actuator is desired. Thebrake actuator utilizes existing hydraulic brake pressure to provide apositive clamping or rotational retention of the multi-disc brakerelative to the axle means to provide a reduction or elimination ofsqueal vibration modes for multi-disc aircraft brakes.

Referring now to the third embodiment of the invention illustrated inFIG. 4, a multi-disc brake indicated generally by reference numeral 80comprises a first plurality of stator discs 86 engaging the torque tube94, a second plurality of discs 88 for engagement with a not shownwheel, a piston housing 102 which includes a plurality ofcircumferentially spaced apart pistons 102a, a bushing 91 disposedbetween a foot or support flange of the torque tube 94 and a thrustsleeve 99, the thrust sleeve 99 extending between a second axiallystationary member or wheel sleeve 96 that engages a bearing assembly 92and an actuator member 98 of a brake actuator indicated generally byreference numeral 90. Brake 80 further comprises a first axiallystationary member or axle sleeve 109 extending between a radial portion87a of axle 87 and the wheel sleeve 96.

The actuator 90 comprises a piston or actuator member 98 received withinan actuation pressure chamber 95 located within piston housing 102.Piston housing 102 includes at least one fluid passage 107 forcommunicating fluid from a bore housing the piston 102a to the actuationpressure chamber 95 and similar passages from the other piston bores.Actuator member 98 includes a seal 98a within chamber 95, and springmeans or Belleville spring 98b located between actuator member 98 andeither a washer or annular member 94c of bolt and nut assembly 95b thatattaches torque tube 94 to piston housing 102. Torque tube 94 includes aflange 94a, and between actuator member 98 and flange 94a is an axialclearance "X".

When piston housing 102 receives brake actuation fluid pressure, thepressure is simultaneously transmitted through passages 107 to theactuation pressure chamber 95. Initially, at an at-rest or at low fluidpressure, the brake 80 is free to rotate relative to the axle 87, suchrotation occurring during extension or retraction of the landing gear.However, when fluid pressure exceeds a predetermined pressure level, theactuator member 98 overcomes the installed load of spring 98b and isdisplaced away from actuation pressure chamber 95, and the pistonhousing reacts by being forced to the left in FIG. 4 such that thepiston housing and its bushing 103 engage axle sleeve 109 which abutsradial portion 87a of axle 87. The actuator member 98 is simultaneouslybiased against thrust sleeve 99 which is held axially stationary bywheel sleeve 96 and bearing assembly 92 anchored by a not shown wheelnut. Thus, piston housing 102 is compressed between the actuator 90 andthe first axially stationary member or axle sleeve 109 (at bushing 103)and radial portion 87a. This compression would dampen vibration andreduce or eliminate squeal vibration during brake operation. Upon thetermination of braking, the spring means 98b will displace the actuatormember 98 leftward when the pressure in actuation pressure chamber 95drops below the predetermined pressure level. Torque tube flange 94aalso serves as an overtravel "stop" for actuator member 98 if the brakeis pressurized before the installation of the brake on the axle 87. Theembodiment of FIG. 4 is similar to that in FIG. 3 in that it can beintegrated and implemented as part of a new brake design. The actuator90 utilizes existing hydraulic brake pressure to provide a positiveclamping or rotational retention of the multi-disc brake relative to theaxle means to provide a reduction or elimination of squeal vibrationmodes for multi-disc aircraft brakes.

We claim:
 1. A multi-disc brake and actuator for vibration damping,comprising a multi-disc brake disposed about axle means and including apiston housing engaging a torque tube, the piston housing and torquetube circumferentially movable relative to the axle means, a firstplurality of discs engaging the torque tube, a second plurality of discsfor engagement with a wheel, the piston housing being located axiallybetween an actuator and a first axially stationary member at the axlemeans, and a thrust sleeve engaging a second axially stationary memberat the axle means, operation of the actuator causing an actuator memberto extend axially and compress the piston housing between the actuatormember and first axially stationary member in order to reducevibrational movement of the piston housing and torque tube relative tothe axle means.
 2. The multi-disc brake and actuator in accordance withclaim 1, wherein the actuator is a hydraulic actuator which receivespressure transmitted simultaneously to said piston housing.
 3. Themulti-disc brake and actuator in accordance with claim 2, wherein apredetermined axial clearance is present between the actuator member andthe torque tube prior to operation of the actuator.
 4. The multi-discbrake and actuator in accordance with claim 3, wherein the actuatorcomprises a portion of the piston housing having therein an actuationpressure chamber and the actuator member displaceable to causecompression of spring means which is compressible at a predeterminedhydraulic pressure such that the member engages the torque tube to causedisplacement of the piston housing and said compression.
 5. Themulti-disc brake and actuator in accordance with the claim 3, whereinsaid spring means is a Belleville washer that provides a pressurelimiter whereby the actuator member is not displaced axially until apredetermined pressure transmitted to the actuation pressure chamber isexceeded.
 6. The multi-disc brake and actuator in accordance with claim5, wherein the spring means provides a return biasing force against theactuator member so that during termination of operation of the actuatorthe actuator member returns axially and reestablishes the predeterminedaxial clearance.
 7. The multi-disc brake and actuator in accordance withclaim 1, wherein the brake includes an axle sleeve located about theaxle and extending axially between a radial portion of the axle and saidsecond axially stationary member, at least a portion of the axle sleevelocated within the thrust sleeve.
 8. The multi-disc brake and actuatorin accordance with claim 1, wherein the brake comprises an aircraftbrake, and the thrust sleeve is located axially between the actuatormember and a wheel sleeve comprising the second axially stationarymember.
 9. The multi-disc brake and actuator in accordance with claim 1,wherein the thrust sleeve is located axially between the second axiallystationary member and the actuator member, and the actuator memberincluding means for sealing between the actuator member and an actuationpressure chamber of the actuator.
 10. The multi-disc brake and actuatorin accordance with claim 9, wherein the second axially stationary membercomprises a wheel sleeve located axially between the thrust sleeve and awheel bearing assembly disposed about the axle.
 11. The multi-disc brakeand actuator in accordance with claim 1, wherein the torque tubecomprises a bushing assembly.